The present invention pertains to a treatment unit with at least two heat sources and a lying surface for the patient.
In open intensive care or even in incubators, heat is additionally supplied to the patient from the outside to compensate the heat balance. As long as only one heat source is used for this, the temperature can still be controlled in a relatively simple manner, because only the heat output of this heat source must be changed. However, as soon as a combination of different heat sources is present, the desired ratio of the heat outputs of the individual heat sources to one another must be determined.
DE 42 04 398 C1 discloses an incubator, in which a first control circuit for setting a certain air temperature is connected to a second control circuit for setting the humidity of the air via a logic circuit in such a way that the set point of the air humidity is automatically adjusted in case of a change in the set point of the air temperature. Two coupled control circuits are thus obtained for different parameters, which cooperate as master-slave control circuits during the conditioning of the ambient air.
The basic object of the present invention is to improve a treatment unit with two heat sources such that the ratio of the heat outputs of the heat sources can be set in relation to one another in a simple manner.
According to the invention, a treatment unit is provided with at least two heat sources and a lying surface for a patient. A first temperature control circuit is provided with a first heat source, a first temperature controller, a first temperature sensor detecting the body temperature of the patient, as well as a first set point setter for the body temperature. A second temperature control circuit is provided for setting the temperature of the lying surface, with a second heat source at the lying surface, a second temperature controller, and a second temperature sensor detecting the temperature of the lying surface. A logic circuit is provided operatively connected between the first temperature control circuit and the second temperature control circuit. The logic unit receives the actual value of the body temperature or the set point of the first control circuit, which is set on the set point setter, as a command variable. The logic unit sends a tracking value for the temperature of the lying surface to the second control circuit via a first logic function.
According to another aspect of the invention, a treatment unit with at least two heat sources and a lying surface for a patient is provided with first and second temperature control circuits. The first temperature control circuit sets the air temperature in the environment of the patient with a first heat source, a first temperature controller, a temperature sensor detecting the actual value of the air temperature within a hood surrounding the lying surface, as well as a first set point setter for the air temperature. The second temperature control circuit sets the temperature of the lying surface, containing a second heat source at the lying surface, a second temperature controller, and a second temperature sensor detecting the temperature of the lying surface. A logic circuit is provided operatively connected to the first temperature control circuit and the second temperature control circuit. The logic circuit receives the actual value of the air temperature or the set point of the first control circuit, which is set on the set point setter, as a command variable, and sends a tracking value for the temperature of the lying surface to the second control circuit via a second logic function.
According to another aspect of the invention, a treatment unit with at least two heat sources and a lying surface for a patient is provided with first and second temperature control circuits. The first temperature control circuit sets the air temperature in the environment of the patient with a first heat source, a first temperature controller, as well as a temperature sensor detecting the actual value of the air temperature within a hood surrounding the lying surface. The second temperature control circuit sets the temperature of the lying surface, with a second heat source at the lying surface, a second temperature controller, and a second temperature sensor detecting the temperature of the lying surface. A third temperature controller is connected to a first temperature sensor, which sends as the actual value a measured value proportional to the body temperature and receives a set point for the body temperature from a third set point setter, and which sends a preset set point for the air temperature to the first temperature controller. A logic circuit receives as the command variable the actual value of the air temperature or the preset set point of the third temperature controller, and sends a tracking value for the temperature of the lying surface to the second control circuit via a second logic function.
To compensate the heat balance of the patient, both an air heater (air temperature) and a lying surface heater are used in open care, but also in closed care in incubators.
If a radiant heater is operated together with a lying surface heater in an open care unit, it is necessary to clarify the question of how high the temperature of the lying surface heater shall be set. The patient without clothes, located on a lying surface, loses the most heat to the environment by radiant, convective and moisture losses. The radiant heater as the only heat source on this side of the body surface above the lying surface must therefore also assume most of the heat supply and compensate the heat losses to the environment to the extent that the patient""s medium-term heat balance is compensated. The radiant heater is normally operated with a skin temperature control unit, which shall maintain the patient at a constant temperature, A temperature sensor is placed for this purpose on the skin of the patient, preferably on the patient""s abdomen. The heat output of the radiant heater now depends on the deviation between the preset set point and the measured temperature of the skin surface. The heat output of the radiant heater can be changed relatively rapidly, because the thermal masses are very small. For example, the time constant of an infrared radiant heater is in the range of 3 minutes to 10 minutes.
Lying surface heaters normally have larger thermal masses and therefore a substantially longer time constant than radiant heaters. A lying surface heater comprises, e.g., an aluminum plate, to the underside of which a heating foil is attached. The aluminum plate ensures good heat distribution in the horizontal direction. A gel mattress, which offers a soft, flexible support, on the one hand, and ensures good heat conduction to the patient, on the other hand, lies on the aluminum plate. The time constant of such a heater is approximately between 30 minutes and 120 minutes. Because of its long time constant, the lying surface heater is not particularly suitable for rapidly changing the temperature of a patient in a closed control circuit. The principal task of the lying surface heater is therefore to minimize the heat losses on the underside of the patient.
As long as the lying surface has the same temperature as the core of the patient""s body, no heat is transported to the patient. The lying surface heater prevents the conductive heat losses to the underside in this case. However, as soon as the patient cools off, the lying surface heater makes a positive contribution to thermal balancing. The heating of undercooled patients is an important use of the lying surface heater. The high temperature gradient of the cold body and the good heat conduction lead to rapid heating of the patient in this case.
The set point for the lying surface heater should be selected, in general, depending on the patient""s body temperature and it should also be 37xc2x0 C. in case of a normal body temperature of 37xc2x0 C.
Provisions are made according to the present invention for providing a first temperature control circuit, which comprises a first temperature controller, a first temperature sensor detecting the patient""s body temperature, a first heat source, and a first set point setter for the body temperature, in a treatment unit for the open care for stabilizing the temperature of the patient. A second temperature control circuit with a second heat source at the lying surface, with a second temperature sensor detecting the temperature of the lying surface, and with a second temperature controller receives the preset set point via a logic circuit from the first temperature control circuit. The logic circuit receives for this the actual value of the body temperature or the set point of the first control circuit, which is set on the first set point setter, as a command variable and sends a tracking value for the temperature of the lying surface to the second control circuit via a first logic function.
In closed care, the air within a hood is circulated with a fan and maintained at a predetermined set point. To set the air temperature, a first temperature control circuit is provided, in which the actual value of the air temperature is detected with a temperature sensor in the environment of the patient and is set to the set point with a first temperature controller.
To set the temperature of the lying surface, a second temperature control circuit is provided, which receives its preset set point via a second logic function from the first temperature control circuit.
The first temperature control circuit supplies for this the set point or the actual value of the air temperature to the logic circuit and the preset set point is generated from this via the second logic function. If a patient temperature, e.g., the body core temperature, is included in the control of the air temperature, an additional temperature controller in the form of a cascade control is advantageously arranged upstream of the first temperature controller, and the additional temperature controller receives the patient temperature as the actual value and forms a command variable by means of a set point of the patient temperature, and the command variable is passed on as a preset set point for the air temperature to the first temperature controller. Corresponding to the measured patient temperature, the preset set point set for the air temperature is increased or decreased by the additional temperature controller. By linking the first temperature control circuit with the second temperature control circuit for setting the temperature of the lying surface, optimal heat supply is obtained for the patient at the lowest possible heat loss.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.